Mutation as cellular process : a Ciba Foundation symposium / edited by G.E.W. Wolstenholme and Maeve O'Connor.

  • Symposium on Mutation as Cellular Process (1969 : London, England)
Date:
1969
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Mutation as cellular process : a Ciba Foundation symposium / edited by G.E.W. Wolstenholme and Maeve O'Connor. Source: Wellcome Collection.

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    CAFFEINE AND U.V. MUTAGENESIS 39 Genetic recombination Crosses were made by mixing i ml of the recipient with o -1 ml of the donor, using logarithmically growing cultures in Difco Nutrient Broth having a titre of about 2 x lo® bacteria/ml. The mixtures were incubated without agitation for loo minutes at 37°, and were then agitated at high speed for one minute on a Vortex mixer to interrupt mating, and various dilutions were plated on the surface of minimal agar plates containing 100 [x g streptomycin/ml and a small amount of Difco Nutrient Broth (1*25 per cent by liquid volume), with or without о • 2 per cent caffeine. This medium was selective for prototrophic recombinants, which were counted after three days. RESULTS Table I summarizes the effects of caffeine on u.v. survival and on the post-irradiation lag in cell division in three classes of strains differing in Her and Exr phenotypes. In all Hcr+Exr+ strains examined, the first post- irradiation cell division was greatly prolonged by caffeine, although the degree of enhancement of the lethal effect of u.v. was variable, and one strain (D13) showed no such enhancement. On the average, both the amount of enhancement of u.v. killing and the time added to the lag in cell division were significantly reduced in the Hcr~Exr+ strains, although in all of these strains caffeine still caused a significant increase in the division lag, and all but one (WWP2 (Hcr~)) showed some enhancement of the lethal effect of u.V. None of the Hcr~Exr~ strains examined showed any lethal synergism between caffeine and u.v., nor did any of these strains take longer to complete the first post-irradiation cell division in the presence of o* i per cent caffeine than in its absence. Thus, excision-defective strains (if they are Exr+) may or may not show residual lethal synergism between o* i per cent caffeine and u.v., but all show residual prolongation by caffeine of the post-irradiation lag in cell division. Table I effects of caffeine in the post-irradiation plating medium on survival and on the lag in cell division No. of Lethal enhancement index* Lag indexf Phenotype strains Range Average Range {min) Average Hcr+Exr+ 6 0-04-1-o 0*35 120-210 170 Hcr-Exr+ 5 о-6-1-5 0-85 36-59 46 Hcr-Exr- 3 i-o i-o о о * % survival on nutrient agar containing o -1 % caffeine at u.v. dose resulting in i % survival on nutrient agar without caffeine. f Minutes added to time required to double initial viable count, after irradiation with u.v. dose resulting in 10% survival on nutrient agar, by adding caffeine (o-1 %) to plating medium (corrected for slight caffeine-induced extension of lag in unirradiated controls).